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All paired up with no place to go: pairing, synapsis, and DSB formation in a balancer heterozygote.

Gong WJ, McKim KS, Hawley RS - PLoS Genet. (2005)

Bottom Line: We have utilized the LacI-GFP: lacO system to visualize the effects of FM7 on meiotic pairing, synapsis, and double-strand break formation in Drosophila oocytes.However, the frequencies of failed pairing and synapsis were still 1.5- to 2-fold higher than were observed for corresponding regions in oocytes with two normal sequence X chromosomes, and this effect was greatest near a breakpoint.We propose that heterozygosity for breakpoints creates a local alteration in synaptonemal complex structure that is propagated across long regions of the bivalent in a fashion analogous to chiasma interference, which also acts to suppress crossing over.

View Article: PubMed Central - PubMed

Affiliation: Stowers Institute for Medical Research, Kansas City, Missouri, United States of America.

ABSTRACT
The multiply inverted X chromosome balancer FM7 strongly suppresses, or eliminates, the occurrence of crossing over when heterozygous with a normal sequence homolog. We have utilized the LacI-GFP: lacO system to visualize the effects of FM7 on meiotic pairing, synapsis, and double-strand break formation in Drosophila oocytes. Surprisingly, the analysis of meiotic pairing and synapsis for three lacO reporter couplets in FM7/X heterozygotes revealed they are paired and synapsed during zygotene/pachytene in 70%-80% of oocytes. Moreover, the regions defined by these lacO couplets undergo double-strand break formation at normal frequency. Thus, even complex aberration heterozygotes usually allow high frequencies of meiotic pairing, synapsis, and double-strand break formation in Drosophila oocytes. However, the frequencies of failed pairing and synapsis were still 1.5- to 2-fold higher than were observed for corresponding regions in oocytes with two normal sequence X chromosomes, and this effect was greatest near a breakpoint. We propose that heterozygosity for breakpoints creates a local alteration in synaptonemal complex structure that is propagated across long regions of the bivalent in a fashion analogous to chiasma interference, which also acts to suppress crossing over.

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DSBs in Oocytes Heterozygous for Three Balancer Chromosomes(A) Representatives from the oocytes with normal or heterozygous balancer chromosomes. Maximum intensity projection of image stacks of nuclei showing C(3)G (red) in conjunction with DNA (blue, DAPI staining) and DSB (green, γ-HIS2AV staining). Bars = 1 μm.(B) Distribution graph representing the number of γ-HIS2AV foci per C(3)G staining nucleus at different developmental regions in germaria. The sample size of oocytes in wildtype is 64, 34, and 9, representing region 2a, 2b, and 3; in FM7/+;SM1/+;TM3/+, 48, 43, and 11; in +/+;SM1/+;TM3/+, 66, 38, and 10, respectively. Data are presented as means ± SD.
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pgen-0010067-g007: DSBs in Oocytes Heterozygous for Three Balancer Chromosomes(A) Representatives from the oocytes with normal or heterozygous balancer chromosomes. Maximum intensity projection of image stacks of nuclei showing C(3)G (red) in conjunction with DNA (blue, DAPI staining) and DSB (green, γ-HIS2AV staining). Bars = 1 μm.(B) Distribution graph representing the number of γ-HIS2AV foci per C(3)G staining nucleus at different developmental regions in germaria. The sample size of oocytes in wildtype is 64, 34, and 9, representing region 2a, 2b, and 3; in FM7/+;SM1/+;TM3/+, 48, 43, and 11; in +/+;SM1/+;TM3/+, 66, 38, and 10, respectively. Data are presented as means ± SD.

Mentions: Data for both γ-HIS2AV staining and C(3)G staining in oocytes doubly or triply heterozygous for these balancers are presented in Figure 7. We saw no obvious difference in either the number of γ-HIS2AV foci per nucleus during the length of meiotic prophase or in the general structure or organization of the SC when comparing wildtype oocytes. This observation suggests that even when confronted with two or three balancer chromosomes, both extensive synapsis and DSB formation still occur in Drosophila oocytes. Moreover, this experiment also suggests that the well-documented ability of heterozygous inversions to increase the frequency of recombination elsewhere in the genome, referred to as the “interchromosomal effect” [28], is not mediated by either a substantial increase in the total number of DSBs or by an obvious change in the timing of their appearance or disappearance.


All paired up with no place to go: pairing, synapsis, and DSB formation in a balancer heterozygote.

Gong WJ, McKim KS, Hawley RS - PLoS Genet. (2005)

DSBs in Oocytes Heterozygous for Three Balancer Chromosomes(A) Representatives from the oocytes with normal or heterozygous balancer chromosomes. Maximum intensity projection of image stacks of nuclei showing C(3)G (red) in conjunction with DNA (blue, DAPI staining) and DSB (green, γ-HIS2AV staining). Bars = 1 μm.(B) Distribution graph representing the number of γ-HIS2AV foci per C(3)G staining nucleus at different developmental regions in germaria. The sample size of oocytes in wildtype is 64, 34, and 9, representing region 2a, 2b, and 3; in FM7/+;SM1/+;TM3/+, 48, 43, and 11; in +/+;SM1/+;TM3/+, 66, 38, and 10, respectively. Data are presented as means ± SD.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1285065&req=5

pgen-0010067-g007: DSBs in Oocytes Heterozygous for Three Balancer Chromosomes(A) Representatives from the oocytes with normal or heterozygous balancer chromosomes. Maximum intensity projection of image stacks of nuclei showing C(3)G (red) in conjunction with DNA (blue, DAPI staining) and DSB (green, γ-HIS2AV staining). Bars = 1 μm.(B) Distribution graph representing the number of γ-HIS2AV foci per C(3)G staining nucleus at different developmental regions in germaria. The sample size of oocytes in wildtype is 64, 34, and 9, representing region 2a, 2b, and 3; in FM7/+;SM1/+;TM3/+, 48, 43, and 11; in +/+;SM1/+;TM3/+, 66, 38, and 10, respectively. Data are presented as means ± SD.
Mentions: Data for both γ-HIS2AV staining and C(3)G staining in oocytes doubly or triply heterozygous for these balancers are presented in Figure 7. We saw no obvious difference in either the number of γ-HIS2AV foci per nucleus during the length of meiotic prophase or in the general structure or organization of the SC when comparing wildtype oocytes. This observation suggests that even when confronted with two or three balancer chromosomes, both extensive synapsis and DSB formation still occur in Drosophila oocytes. Moreover, this experiment also suggests that the well-documented ability of heterozygous inversions to increase the frequency of recombination elsewhere in the genome, referred to as the “interchromosomal effect” [28], is not mediated by either a substantial increase in the total number of DSBs or by an obvious change in the timing of their appearance or disappearance.

Bottom Line: We have utilized the LacI-GFP: lacO system to visualize the effects of FM7 on meiotic pairing, synapsis, and double-strand break formation in Drosophila oocytes.However, the frequencies of failed pairing and synapsis were still 1.5- to 2-fold higher than were observed for corresponding regions in oocytes with two normal sequence X chromosomes, and this effect was greatest near a breakpoint.We propose that heterozygosity for breakpoints creates a local alteration in synaptonemal complex structure that is propagated across long regions of the bivalent in a fashion analogous to chiasma interference, which also acts to suppress crossing over.

View Article: PubMed Central - PubMed

Affiliation: Stowers Institute for Medical Research, Kansas City, Missouri, United States of America.

ABSTRACT
The multiply inverted X chromosome balancer FM7 strongly suppresses, or eliminates, the occurrence of crossing over when heterozygous with a normal sequence homolog. We have utilized the LacI-GFP: lacO system to visualize the effects of FM7 on meiotic pairing, synapsis, and double-strand break formation in Drosophila oocytes. Surprisingly, the analysis of meiotic pairing and synapsis for three lacO reporter couplets in FM7/X heterozygotes revealed they are paired and synapsed during zygotene/pachytene in 70%-80% of oocytes. Moreover, the regions defined by these lacO couplets undergo double-strand break formation at normal frequency. Thus, even complex aberration heterozygotes usually allow high frequencies of meiotic pairing, synapsis, and double-strand break formation in Drosophila oocytes. However, the frequencies of failed pairing and synapsis were still 1.5- to 2-fold higher than were observed for corresponding regions in oocytes with two normal sequence X chromosomes, and this effect was greatest near a breakpoint. We propose that heterozygosity for breakpoints creates a local alteration in synaptonemal complex structure that is propagated across long regions of the bivalent in a fashion analogous to chiasma interference, which also acts to suppress crossing over.

Show MeSH
Related in: MedlinePlus